You *never* buy 200+ 18' bolts without specifying their performance. Each bolt probably costs more than $10K, so it's a multi-million contract.
Here is the machine that you use for testing metals for strength. This is just a well instrumented hydraulic press, backward. Samples of special shape are made, and then the machine pulls on them, accurately recording the tension and the deformation. This gives you the stress–strain curve. Eventually the sample breaks.
Even if the company that made bolts doesn't have such a machine, it would be sheer insanity to buy a hundred tons of steel without sending a sample to an independent lab for these tests. You would want a chemical and a crystallographic analysis in addition to that. This is what the engineers did after the bolts failed; that's why they are telling us that the steel was wrong (not the right type, or the right type made incorrectly.)
Now the manufacturer of those bolts is going to lose their shirt on this deal. I'm sure their profit margin is not fat enough to cover redoing all bolts and still staying in black.
Defective parts or defective design? More stress on the bolts than the engineer predicted?
You could, and should, do a simple nondestructive hardness test on the material being used to make the bolts before the bolts are made and before any other test are done.
You could do a hardness test on enough material to make 288+ bolts in about 2 days max.
That would tell you if the material is up to specs before wasting any more time or money on it.
Too soft or too hard chunk it.
No point in spending any more time or money making a bolt when it’s going to be junk anyway.
Thank you most kindly for your informative response.